The present invention relates to a stack mold stabilizer and more particularly to a device for maintaining an equal distance between the mold plates in a stack mold.
Molds have long been used for injection molding plastic articles by bringing opposed faces of adjacent mold plates into abutting contact with each other. As is well known, opposed faces of adjacent mold plates define one or more cavities conforming to the desired product. When the opposed faces of adjacent mold plates are brought together, molten plastic is injected into the cavity through a conduit in one of the mold plates. The mold plates are cooled to cause the molten plastic to solidify to the desired shape. The mold plates are then separated and the finished plastic article is ejected. Closing and opening the mold plates to produce the finished plastic articles is performed on a continuously reciprocating basis.
It has been found that production of plastic articles can be substantially increased by arranging three or more mold plates in a stack mold and injecting the molten plastic into the cavities between opposed faces of adjacent mold plates. The mold plates are then separated to eject finished plastic articles from the mold. For a stack mold to operate properly, the mold plates must have equal spacing between them at all times.
Various prior art devices have been used in an attempt to maintain such equality. One example is the use of hydraulic actuator devices. A first hydraulic actuator is typically coupled between the fixed mold plate and the center mold plate of the stack. A second hydraulic actuator is coupled between the center mold plate and the driven mold plate. The hydraulic actuators are idling in the sense that no external fluid pressure source is applied to them.
As the driven mold plate is reciprocated by a suitable driving force, hydraulic fluid flows between the actuators to maintain the mold plates properly aligned. While such a system operates effectively when all parts thereof are functioning properly, difficulties have been experienced.
For example, such hydraulic actuator devices have been found to require a great deal of maintenance. The hydraulic seals leak thereby permitting air to enter the actuator system. This entry of air into the systems causes the center mold to become misaligned with respect to the opposed faces of the fixed mold plate and the driven mold plate. The driving source applies a very substantial pressure to the driven mold plate and if there is any misalignment between the mold plates, the hydraulic actuators may be damaged. Thus, the seals of the hydraulic actuators must be constantly replaced and hydraulic fluid must be constantly replenished in the cylinders. Bleeding air from the hydraulic actuators is constantly required even under the best of operational circumstances.